Optical printer

An optical printer is a device consisting of one or more film projectors mechanically linked to a movie camera. It allows filmmakers to re-photograph one or more strips of film. The optical printer is used for making special effects for motion pictures, or for copying and restoring old film material.

Common optical effects include fade outs and fade ins, dissolves, slow motion, fast motion, and matte work. More complicated work can involve dozens of elements, all combined into a single scene.

The first, simple optical printers were constructed early in the 1920s. Linwood G. Dunn expanded the concept in the 1930s, and during World War II he was commissioned by the United States armed forces' photographic units to design an optical printer that could be ordered as a stock item like a camera. Development continued well into the 1980s, when the printers were controlled with minicomputers. Prime examples of optical printing work include the matte work in Star Wars (1977).

In the late 1980s, digital compositing began to supplant optical effects. By the mid-nineties, computer graphics had evolved to rival and surpass what was possible with optical printers, and many now consider optical printing all but obsolete. Improvements in film scanners and recorders allow for a complete feature film to be processed by computers, have special effects applied, and then be processed back to film.

Today, optical printing is mostly used as an artistic tool by experimental film makers, for educational purposes, or for photochemical (as opposed to digital) film restoration. As a technique, it is particularly useful for making copies of hand painted or physically manipulated film.

...
Wikipedia